How to map a texture?

radiance-general
1

Hi, Dear friends:

I am trying to map pictures to simulate the texture of wood, carpet and so on.
I use ra_tiff to convert a .tif picture into a .pic picture, and then use colorpict to map it such as:

void colorpict image01
9 clip_r clip_g clip_b 02.pic picture.cal frac(U) frac(V) -s 500
0
0

image01 plastic wood_mat
0
0
5 .8 .8 .8 .02 0

I found that the properties of plastic material like "5 .8 .8 .8 .02 0" influence the result greatly. how should I set them properly?

Thanks a lot.

Yours,

Huang

2

Hi Huang,

Picture normalization is spelled out in the sidebar on page 262 of "Rendering with Radiance"

     http://radsite.lbl.gov/radiance/book/

I have reprinted the sidebar below for your convenience:

There are generally two cases in which pictures are applied as patterns. In the first case,
the picture corresponds to a piece of artwork or some printed material, and only a sin-
gle copy of it is mapped into the scene. The type of picture that is appropriate is
usually one whose pixel values correspond to reflectances, so the average value will vary
depending on average reflectance. The clip() function is often used for value map-
ping to ensure that reflectances do not exceed 1. In the second case, the picture
corresponds to a repeating pattern on some larger surface, such as a tiled floor. The
type of picture appropriate is usually normalized to an average value of 1, so that the
material primitive will carry the average reflectance. The noop() function is usually
specified for value mapping, since the reflectance multipliers may take on arbitrary
values (corresponding to highlights, for instance). Be aware, when you are using these
files, of which type of picture you have. This is most easily determined by displaying
them with ximage or some similar display program. If about half their values are
greater than 1 (washed out so −e−1 makes them look about right), they are normal-
ized images for tiling. (See the normpat manual page on the CD-ROM for additional
information.)

The normpat man page may be found here:

     http://radsite.lbl.gov/radiance/man_html/normpat.1.html

Additional information about mapping picture coordinates on page 259 of RwR.

-Greg

···

From: "Huangwx@Kyoto-Univ." <[email protected]>
Date: June 15, 2005 7:11:56 PM PDT

Hi, Dear friends:

I am trying to map pictures to simulate the texture of wood, carpet and so on.
I use ra_tiff to convert a .tif picture into a .pic picture, and then use colorpict to map it such as:

void colorpict image01
9 clip_r clip_g clip_b 02.pic picture.cal frac(U) frac(V) -s 500
0

image01 plastic wood_mat
0
5 .8 .8 .8 .02 0

I found that the properties of plastic material like "5 .8 .8 .8 .02 0" influence the result greatly. how should I set them properly?

Thanks a lot.

Yours,

Huang

3

I seem to remember Lightscape having a handy feature that would give you what it thought you should be using based on the individual images. My guess is that it was simply averaging the pixels together to come up with an average RGB value. I've done similar things with photoshop, but this method is a far cry from what the actual measured reflectances would be, and is only a visual attempt at getting it close.

.8 .8 .8 sounds too high for wood. I think wood (depending on the type is around ~.2 to ~.4 depending on the wood). Check your radiance's lib directory. I believe there are some old materials files that include wood definitions.

Hope that helps.

Mark

Hi, Dear friends:

I am trying to map pictures to simulate the texture of wood, carpet and so on.
I use ra_tiff to convert a .tif picture into a .pic picture, and then use colorpict to map it such as:

void colorpict image01
9 clip_r clip_g clip_b 02.pic picture.cal frac(U) frac(V) -s 500
0
0

image01 plastic wood_mat
0
0
5 .8 .8 .8 .02 0

I found that the properties of plastic material like "5 .8 .8 .8 .02 0" influence the result greatly. how should I set them properly?

Thanks a lot.

Yours,

Huang
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